Filter element for filtering a fluid and a filter unit formed therefrom

ABSTRACT

A filter element for filtering a fluid comprises a first clamping ring with an outer ring; a first filter disk; a first inner support plate for supporting the first filter disk and which faces to the outside or to an inner flow channel; a second inner support plate provided with recesses; a second filter disk arranged adjacent the second inner support plate; and a second clamping ring which is connected to the first clamping ring by connecting elements. The filter disks and the inner support plates are arranged inside a housing which is formed by the clamping rings, by at least one outer ring and by outer support plates provided with recesses and covering the filter disks on the outside.

The invention relates to a filter element for filtering a fluid and afilter unit formed therefrom with the features of the preamble of claim1.

Usually flat screen elements are used for filtering high-viscosity mediasuch as plastic melt. Contaminants in the plastic melt such as aluminumparticles or paper residue are deposited in the filter media of thefilter elements. The effective filter surface is essentially limited tothe opening cross-section of the screen cavity and is directly relatedto the size of the filtration device, for example with a screen pistonchanger.

To overcome this disadvantage, filter elements such as the onesdescribed in DE 42 12 928 A1 are used successfully. The disk shape andthe plurality of stacked individual disk filter elements can increasethe effective filter surfaces considerably in such a filter unit.

In particular for the filtration of plastic melts, the filter units areplaced in a screen cavity of a so-called “screen piston changer”.However, it was observed that the individual filter elements can bendaway with the existing fluid pressure, which can lead to blocking ofindividual flow paths as well as to damage and subsequent leakage of thefilter element.

With increasing contamination, the melt flow is redirected to anotherscreen cavity with a different filter element in many screen pistonchangers. While the production flow is maintained via the latter, thecontaminated filter unit can be freed of the adhering particles througha backwash procedure. For this purpose, a part of the melt is guidedthrough the filter elements of the filter unit in a direction oppositeto the one during normal operation such that the particles adhering tothe filter media of the filter elements are loosened and rinsed away.

However, the backwash procedure that is possible with normal flat screenelements is not possible with the filter elements of the generic kindusing multiple disk filters because the fine metallic filter mesh of thefilter elements is not supported in the reverse direction of flow andthus could tear during a backwash.

The problem addressed by the present invention is therefore to develop afilter element of the type described above such that bending of thefilter elements is avoided during production operation and thus to allowa backwash.

This problem is solved by a filter element with the features of claim 1.

In terms of the invention, a “ring” does not only refer to circularshapes but also to closed lines of other shapes such as ellipses oroblong or polygonal contours.

The inner support plates support the filter mesh against the fluidpressure, which acts preferably from the outside during productionoperation. With the flow direction during production operation, thefilter disks lay with a part of the outer edge area lengthwise to thefluid or the plastic melt arriving at the mesh of the filter disk fromthe outside and dirt is retained on the outside. The flow continuesthrough the recesses of the inner support plates and into the cavity ofthe filter element.

Additionally provided are support plates provided with recesses suchthat the filter disks are covered both towards the inside as well as onthe outer sides of the filter element and/or can be supportedtwo-dimensionally. This allows for a change in the flow direction, i.e.,also backwash operation during which build-up is rinsed off the filterdisk during the reversal of the flow direction.

The structure of a filter element according to the invention is veryrobust. The filter element can be easily disassembled and cleaned, inparticular it can be subjected to thermal treatment without beingdamaged, for example to burn off plastic melt residue.

In addition, the support plates are preferably kept at a distance fromeach other by at least one spacer element located on the inside suchthat an inner hollow space is kept open even at high pressures serves asa flow channel and is open toward the edge of the central bore hole ofthe filter element.

The spacer elements can be spider web-shaped or wheel-like structuresthat need to be inserted separately. However, they may also be formedthrough protruding ledges at the housing ring, clamping ring or outerring.

The spacer elements may also be formed by curved support plates, whichexpand concavely or convexly when viewed in the direction of the flow,whereby the curvatures are facing each other such that they contact eachother in part, for example with concave shapes in the center and withconvex shapes in the peripheral edge regions with the remaining surfaceareas of the support plates being kept at a distance from each other.

Due to its flexibility, the filter mesh can easily adapt to thethree-dimensional shape of the support plates such that it remainssupported even if the support area is not in one plane.

The outer support plates can be curved as well, once on the inside tofollow the shape of the inner support plates in order to avoid too bigan expansion in the filter mesh located in between and to keep itsupported over the entire area in both flow directions. In addition, acurvature protruding toward the outside can support an outer flowchannel in the same manner by the curvature of at least one filterelement resting against an adjacent filter element.

The respective curved inner and outer surfaces of the inner and outersupport plates must not necessarily be parallel to each other, i.e., thesupport plates must not necessarily be designed in the manner of adeep-drawn sheet metal but can also form a bulbous body on both sides.

The connection elements are preferably screws with screw heads and nutssuch that disassembly and assembly can be accomplished easily andeverywhere with existing tools.

Only the filter disks are wear parts that must be replaced when theirmetallic and potentially multi-layered filter mesh is badly damaged.

The outer support plates may each be integrated in the clamping ring.However, they can also be placed under the clamping ring as separateplates.

The support plates are preferably designed as perforated plates that areeasy to manufacture and allow for small area support of the filter meshthrough their grid structure.

The filter disks preferably have an inner ring and an outer ring, whichare preferably made of a non-ferrous metal in particular of copper. Thiscreates a metallic seal, once at the inner circumference as a sealagainst a support tube located on the inside on which the filterelements are stacked and once at the outer circumference as a sealagainst the outer ring.

It is also possible to manufacture the ring-disk-shaped filter disksover-dimensioned at the inner and/or outer edge compared to the adjacentcomponents and then to press them appropriately onto the adjacentcomponents.

The outer ring can be designed in one place with the clamping ring orthe inner support plate.

One preferred embodiment of the invention provides the use of similarinner support plates that arrive at the outer circumference each in thecenter of a partial outer ring. This results in a T-shaped cross-sectionat the edge of each inner support plate. To form a filter element, twopieces each of a total of three similar parts can be used, namely twoidentical inner support plates with a partial outer ring, two identicalfilter disks and two identical outer support plates, which at the sametime integrate the clamping ring on the edges. This enablescost-effective manufacturing and storage as well as simple handling.

A filter unit built of several filter elements according to theinvention as in claim 12 can be built easily and also disassembledeasily for cleaning purposes because the filter elements according tothe invention are not sensitive to knocks and hits due to their massiveouter housing consisting of outer ring, support plates and clampingrings.

By the fact that the connection elements protrude at the face sides ofthe finished filter element, the protrusions can at the same time alsoserve as spacers forming flow channels between adjacent filter elements.Thus, filter elements stacked on top of each other support each otherand cannot be bent away by the fluid pressure.

One preferred embodiment provides for an additional coarse filter thatencloses the filter elements and that extends between the bottom of thefilter unit and the bottom of the screen cavity, into which the filterunit is placed, and its head plate.

The coarse filter element retains, for example, particles such asaluminum or paper residue, which are present in particular duringplastic recycling and which may be sufficient in size that they nolonger or only with great difficulty can be removed from the flowchannel between the filter elements by back-washing. This achieves acascade filtration where coarse particles can no longer reach the insideof the actual filter unit. The task of the latter is then limited to theseparation of fine items or agglomerates, which leads to a significantlyincreased service life.

Below, the invention will be explained in greater detail with referenceto the drawing. In detail, the Figures show:

FIG. 1 an exploded view of a filter element according to a firstembodiment;

FIG. 2 a perspective view of an assembled filter element according tothe first embodiment;

FIG. 3 a section of several filter elements stacked on a support tube,and

FIG. 4 a detail from the edge of a sectional view of a second embodimentof a filter element; and

FIG. 5 a detail from the edge of a sectional view of a third embodimentof a filter element.

FIG. 1 shows a filter element 100 with its components in correctposition arrangement prior to assembly.

The main components from right to left in the order of assembly are:

A clamping ring 10 with a through-hole 11 for accepting screws, with anintegrated cylindrical outer ring 14 and an integrated support plate 12.

A first ring-disk-shaped filter disk 30, which is bordered at its inneredge by an inner ring 31 and at its outer edge by an outer ring 32, saidrings 31, 32 being made of a copper profile.

A first support plate 40 being designed as a serrated disk.

A spacer element 50 that keeps the first inner support plate 40 at adistance from a second inner support plate 40.

A second filter disk 30.

A clamping ring 20 with through-holes for accepting screws 21. In thisembodiment, the clamping ring 20 has an integrated central support plate22 as does the clamping ring 10.

FIG. 2 shows the fully assembled filter element 100. Visible therein isthat where the spacer element 50 is arranged in the center, a flowchannel 102 is formed at the finished filter element 100 and is opentowards the edge of the inner receiving bore hole 101.

FIG. 3 shows a stack of a total of three filter elements 100 that aremounted on a support tube 130 indicated only schematically. The innerrings 31 of the filter disks 30 rest tightly on the outer surface of thesupport tube 130. The outer rings 32 produce a seal against the innersurface of the outer ring 14. Through the screw heads and the screwshaft protrusions or the nuts, respectively, adjacent filter elements100 are kept at a distance from each other forming an outer flow channel103 between two filter elements 100.

The flow direction during production operation is as indicated by thearrows: From the outer circumference of the filter unit 100 into theouter flow channels 103; from there through the filter disks 30 to theinner flow channels 102. The latter are open towards the centralreceiving bore hole 101 in the filter elements 100 as can be seen inFIGS. 2 and 4. In this manner, the fluid can discharge through the boreholes 131 in the tube casing of the support tube 130 into its innerspace 130.

FIG. 4 shows a detail from the edge area of a filter element 100′according to a second embodiment. The inner support plate 40′transitions smoothly into a partial outer ring 14′ such that a T-shapedcross-section is created in the edge area of this unit.

Through the preferably mirror-symmetrical design, the two identicalsupport plates 40′ with the partial outer ring 14′ can be used for bothsides. A spacer ring 50′ is clamped in-between and ensures a seal of theinner cavity 102′ towards the outer circumference. To enable the seal,the distance ring 50′ has a greater height than the two protrusions ofthe partial outer ring 14′ that point inward together. Thus, an air gap13′ remains between the partial outer rings 14′. This allows forsecuring to each other two identical units of outer support plates 12′,filter elements 30′ and inner support plates 40′ by enclosing a spacerring 50′ using a screw connection, which is here only indicated, suchthat a complete filter element 100′ is created, which is a unit that issealed towards the outside. The outer support plates 12′ are designed asclamping rings 10′ at their outer edges, i.e., they do not have anopening towards the inner cavity in this area but only recesses toreceive the screws and other connection elements.

FIG. 5 shows a third embodiment of a filter element 100″, which at theedge is designed like the second embodiment of the filter element 100″described above, namely with partial outer rings 14″, which on theoutside follow the inner support plates 40″. However, in this exemplaryembodiment, the support plates 40″ have a concave curvature relative tothe flow direction from the outside to the inside. The protruding areascontact each other, however, the concave areas are preferably notring-shaped across the entire partial circle but rather consist ofseveral individual humps such that radial flow paths will also remainopen from the outer areas of the cavity 102′ towards the outlet openingat the inner edge.

With this exemplary embodiment, the outer support plates 12″ with theintegrated clamping rings are flat at the outer surface and are parallelto the contour of the inner support plate on the inside. In this manner,an also three-dimensionally curved filter element 30″ that is sandwichedin between is supported in both flow directions without over-extending.

What is claimed is:
 1. Filter element for filtering a fluid, saidelement comprising, in combination: (a) a first clamping ring with anouter ring; (b) a first filter disk; (c) a first inner support plateprovided with recesses for supporting the first filter disk, said firstinner support plate facing to the outside or an inner flow channel; (d)a second inner support plate provided with recesses; (e) a second filterdisk arranged adjacent the second inner support plate; and (f) a secondclamping ring which is connected to the first clamping ring by means ofconnection elements, wherein the filter disks and the inner supportplates are arranged inside a housing which is formed by the clampingrings, by at least one outer ring and by outer support plates providedwith recesses and covering the filter disks on the outside.
 2. Thefilter element defined in claim 1, wherein at least one spacer elementis arranged between the inner support plates to form the inner flowchannel.
 3. The filter element defined in claim 1, wherein at least oneinner support plate is designed at least on its inside with a curvatureto support the inner flow channel.
 4. The filter element defined inclaim 1, further comprising at least one outer support plate which iscurved at its inner surface.
 5. The filter element defined in claim 1,further comprising at least one outer support plate which is curved atits outer surface.
 6. The filter element defined in claim 1, furthercomprising at least one outer support plate which is integrated with theclamping ring.
 7. The filter element defined in claim 1, wherein thefilter disk comprises an inner ring and an outer ring, with at least onering-shaped filter medium supported between them.
 8. The filter elementdefined in claim 7, wherein at least one of the inner ring and the outerring of the filter disks is made of nonferrous metal.
 9. The filterelement defined in claim 1, wherein the filter disk has a ring-diskshape and is under-sized at its inner edge relative to the outerdiameter of a support tube arranged on the inside and is over-sized atits outer edge relative to the inner diameter of the outer ring.
 10. Thefilter element defined in claim 1, wherein the outer ring is designed in11. The filter element defined in claim 1, wherein the first and secondinner support plates are similar in size and shape and wherein, theouter circumference of each support plate terminates at the center of apartial outer ring, thereby forming a T-shaped cross-section in therespective edge region thereof.
 12. Filter unit for a filtering device,comprising: a support tube having a tube casing and having severalrecesses in the tube casing; and a plurality of stacked filter elements,with each filter element as defined in claim 1, which are centered onthe support tube, wherein the connection elements protrude outwardsbeyond the clamping ring and wherein through their protrusions an inletflow channel is formed between adjacent filter elements, said flowchannel continuing in a flow channel that runs through the filter disksinto the inner flow channel of the filter elements to at least onerespective recess in the support tube; and wherein a head plate isarranged adjacent the support tube and covers the stack of filterelements.
 13. The filter unit as defined in claim 12, further comprisingan additional coarse filter element that encloses the filter elementsand that extends between a bottom of the filter unit, or a bottom of ascreen cavity into which the filter unit is placed, and a head plate ofthe filter unit.